Introduction to Dermatology 1 Flashcards
The skin arises due to juxtaposition of which two major embryological elements?
Epidermis and the Dermis
What does the epidermis originate from?
The ectoderm
What does the dermis originate from?
The mesoderm which comes into contact with the inner surface of the epidermis
What is the mesoderm essential for enducing?
The differentiation of epidermal structures
What is the epidermis formed as by week 5?
A single basal layer of cuboidal cells
What is the periderm?
A secondary layer of squamous, non-keratinizing cuboidal cells which sits on top of the basal layer of the epidermis
When does the periderm develop?
Week 5
What is the vernix caseosa?
A white waxy protective substance which covers the skin during the last trimester of fetal development
What happens to the basal layer of cuboidal cells from week 11?
The stratus germinativum proliferate to form a multi-layered intermediate zone which consists of four more superficial strata
What are the four superficial strata called?
The Spinosum, granulosum, lucidum and corneum
Where is the stratum lucidum found?
On the palms of hands and the soles of feet
What are dermal papillae?
When the epidermal ridges protrude as troughs into developing dermis beneath neurovascular supply
When does the development of hair follicles occur?
Between weeks 9-13
In which superficial stratum layer do hair follicles develop?
In the stratum germinativum
What is lanugo hair?
soft, feathery hair that can grow all over the body, most often on the back and shoulders.
What cells is the epidermis composed of?
Keratinocytes
How long does the progression from stratum basale to Stratum corneum take?
30-40 days
What is the order of cellular progression of cells in the epidermis?
Starts with basale - then Spinosum, Granulosum, Lucidum and finally Corneum
What process is accelerated in skin conditions like psoriasis?
The cellular progression from the basal layer
What happens to the morphology of the epidermal cells as they progress from basal layer to Stratum Corneum?
They become progressively flatter
What are the special features of the stratum corneum?
They lack nuclei or organelles
What does the filamentous cytoskeleton of keratinocytes consist of?
Actin containing microfilaments
Tubulin-containing microtubules
Intermediate filaments (keratins)
What are the five roles of keratins?
Structural properties
Cell signalling
Stress Response
Apoptosis
Wound Healing
What are desmosomes?
Major adhesion complex in the epidermis which anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes
What do desmosomes provide the epidermis with?
Resilience -allow the withstanding of trauma
What are gap junctions?
Clusters of intercellular channels (connexons) which allow connections between cytoplasm of adjacent keratinocytes
What are gap junctions essential for?
Cell synchronization, cell differentiation, cell growth and metabolic coordination
What do adherens junctions engage with?
Actin skeleton
What is the primary role of tight junctions?
They are important in maintaining barrier integrity and cell polarity
what are melanocytes?
They are dendritic cells which distribute melanin pigment to keratinocytes
How does the number of melanocytes change between different ethnicities?
The number of melanocytes does not change, however the amount of pigment they produce does vary
What four other cells are present in the epidermis aside from keratinocytes
Melanocytes, Langerhans cells, Merkel cells and Mast cells
What are Langerhans cells?
Dendritic cells which are antigen presenting and found in the epidermis
What are Merkel Cells?
Mechanosensory receptors
What sits under the epidermis layer?
Basement membrane
What is the basement membrane also known as?
The dermal-epidermal junction
What is the dermal-epidermal junction composed of?
Proteins and glycoproteins including type 4 & 7 collagens, laminin and integrins
What is the role of the basement membrane?
Involved in cell adhesion and cell migration
What layer of the skin is under the basement membrane?
The dermis
How does the dermis arise?
From mesoderm which comes into contact with the inner surface of the epidermis
What are the two layers the dermis is split into?
Papillary dermis and Reticular dermis
What aspect of the dermis layer provides resilience?
The supporting ECM
Which layer of the dermis is closest to the epidermis?
The papillary dermis
Which dermal layer is highly vascular?
Papillary dermis
What is the reticular dermis composed of?
Dense connective tissue
Which dermal layer forms the bulk of the dermis?
The reticular dermis
What is the papillary dermis composed of?
Loose connective tissue
Which proteins are present in the dermis?
Collagen and elastic fibres (fibrillin and elastin)
Which collagen types are present in the dermis?
Type 1 and Type 3
What are the three glycoproteins found in the dermis?
Fibronectins, fibulin and integrins
What do the glycoproteins found in the dermis do?
They facilitate cell adhesion and cell motility
What is the ground substance found in the dermis composed of?
Glycosaminoglycan and proteoglycan
What does the ground substance lie between?
The dermal collagen and elastic tissue
What are the primary cells present in the dermis?
Fibroblasts
What do fibroblasts do?
Make collagen
What cells aside from fibroblasts are present in the dermis?
Histiocytes, mast cells, neutrophils, lymphocytes and dermal dendritic cells
What does the subcuteanous layer contain?
Connective tissue and fat
What are melanocytes derived from?
The neural crest
Does the blood supply cross into the epidermis?
No
Describe the vascular supply of the skin?
The blood supply runs deep - composed of superficial vascular plexus which runs in the dermis
Which dermal layer has more vascular supply?
papillary dermis - the superficial dermal layer
What is the innervation of the skin composed of?
Both sensory and autonomic components
What two autonomic components are involved in the innervation of the skin?
Cholinergic and Adrenergic
What is meant by eccrine?
Opens directly onto the surface of the skin
What is meant by apocrine?
Apocrine sweat glands, which are usually associated with hair follicles, continuously secrete a fatty sweat into the gland tubule
What innervation do apocrine glands receive?
Adrenergic
What is a pilosebaceous unit?
A structure consisting of hair, hair follicle, arrector pili muscle and sebaceous gland
Which areas of the skin receive more innervation than any where else?
Face, extremities, genitalia and hands
Describe the innervation found in the superficial dermis?
A branching network, often accompanying blood vessels which forms a mesh of interlacing nerves
What are the two types of nerve endings?
Corpuscular and free
What type of receptors are found in free nerve endings
Non-encapsulated receptors
What type of receptors are found in corpuscular nerve endings?
Encapsulated receptors
Which layer of the skin are non-encapsulated receptors found in?
Epidermis
Which layer of the skin are encapsulated receptors found in?
Dermis
What are two examples of encapsulated receptors?
Pacinian and Meissners
What is a Meissner corpuscle?
It is an encapsulated, unmyelinated mechanoreceptor
Where are Meissner’s corpuscle located, and where are they most concentrated?
Located in the superficial dermis and most concentrated in thick, hairless skin eg finger pads and lips
What do Meissner Corpuscles help to detect?
Light touch and slow vibration
What is another name for Meissners Corpuscle?
Tactile Corpuscle
What is a Ruffini Corpuscle?
A slow acting mechanoreceptor
Where is the Ruffini Corpuscle found?
Deeper in the dermis
What shape are Ruffini Corpuscles?
Spindle shaped
What are Ruffini Corpuscles sensitive to?
Skin stretch
Where are Ruffini Corpuscles found with the highest concentration?
Around fingernails
What do Ruffini Corpuscle monitor?
The slippage of object
What is a Pacinian Corpuscle?
An encapsulated, rapidly adapting mechanoreceptor
What are Pacinian Corpuscle involved in sensing?
Deep pressure and vibration
What is the shape of Pacinian Corpuscle?
Ovoid
Where are Pacinian Corpuscle most commonly found?
In the dermal Papillae of hands and feet
What is the Merkel Cell derived from?
A modified keratinocyte
What are Merkel cells used to detect?
Light and sustained touch, pressure
What layer of the epidermis are Merkel cells found?
Basal layer
Where are Merkel cells most populous?
In fingertips
Aside from fingertips, where else are Merkel cells found?
In the palms, soles, and oral and genital mucosa
What nerve ending helps to detect pain?
Noicoreceptors
What nerve ending helps to detect temperature?
Thermoreceptors
What three microbiota are found in the skin?
Bacteria, fungi and viruses
What is the role of the microbiome of the skin?
Immune modulation and epithelial health
What are the predominant bacteria found in the microbiome of skin?
Actinobacteria, Firmicutes and Bacteroidetes and Proteobacteria
Is the microbiome involved in disease?
Yes
what are the 6 functions of the skin?
Immunological Barrier
Physical Barrier
Thermoregulation
Sensation
Metabolism
Aesthetic Appearance
What are the important immune cells in regards to the skin functioning as a immune barrier
Langerhans cells
Which cells acts as sentinel cells in the epidermis
The langerhans cells
How do Langerhans cells act against infection?
They initiate the immune response to microbial threats by detecting PAMPs
How are the dendritic processes of the Langerhans cells extended?
Through intercellular tight junctions to sample the outermost layer of the skin - stratum corneum
Which cells do Langerhans cells promote the expansion and activation of?
Skin resident regulatory cells (Tregs)
Which cells carry out immune surveillance in the dermis?
Tissue-resident T cells, macrophages and dendritic cells
What are the two keratinocyte derived endogenous antibiotics that are involved in the innate immune defense against bacteria and viruses?
Defensins and Cathelicidins
What does the cornified cell envelope and stratum coneum restrict?
Water and protein loss from the skin
What is one of the most toxic substances which the skin acts as a barrier against?
UV
How does the skin protect against UV-induced DNA damage?
Melanin helps prevent UV from actioning its mutagenic property
How does subcutaneous fat act as a physical barrier?
It acts as a shock absorber, helps cushion trauma
What happens when the skin loses the ability to restrict water and protein loss?
Leads to dehydration which can cause pre-renal failure and high-output cardiac failure
What type of sweat does eccrine glands secrete?
Salty sweat
Where are apocrine glands most commonly found?
In the axilla and groin
How does the skin regulate heat loss?
Through vasodilation and vasocontriction in deep or superficial vascular plexuses
Which glands are involved in the cooling effect?
Eccrine glands
What happens to the superficial vascular plexuses when we want to lose heat?
Vasodilation
How do we lose heat through vasodilation/constriction?
radiation
Aside from thermoregulation, what are the glands also important in?
Fluid regulation
Synthesis of what metabolic compound occurs partially in the skin?
Vitamin D
What percentage of total body fat is stored in the subcutaneous fat?
80%
How does subcutaneous fat have metabolic functions?
It acts as a calorie reserve
Which hormone is found in the subcuteaous fat?
Leptin
What does the hormone leptin do?
Acts on hypothalamus to regulate hunger and energy metabolism
What occurs when you do not produce leptin?
You have an insatiable appetite, gain unnecessary amount of adipose tissue = fat
What psychological impact can skin have?
Leads to feels of low self worth, feeling “ugly”, not wanting to get into romantic relationships, increased risk of suicide
What skin condition can cause renal failure?
Transepidermal fluid loss
